I am not sure if it is the resister or the switch. It works on the top two settings but not on the bottom two settings. I would believe it is the switch but read that it could be the resister. It is a 2002 Jeep TJ. I am just looking for some more insight to the problem.

 

This was posted in the Liberty section, might help.
The fan on my 2002 Liberty suddenly quit working on the 1-2 speed settings. This is the second time that this has occurred in two years. The problem is caused by a failed resistor in the heater ducting, what this resistor is for is beyond me. It is located behind the glove-box and is easy to replace. Open the glove box and press in the tabs at either side of the box, this will lower the box right down making the resistor readily accessable, it may be a good idea to empty the contents of the box first, as I found out. You will see a wire harness block on the right-hand side of the glove box opening, this is quite difficult to get off as there are clips on the top and bottom. Once the wiring block has been removed, remove the top and bottom screws holding the resistor in place and pull it straight forward from the ducting. The replacement part #05139719-AA (cost 29.25 CAD + tax of course!!) should be available at your nearest Chrysler dealer this is a common replacement part on Jeep Liberty's. It took me about 15 minutes to replace this part and the fan once again works on all speed settings.